Cement-like materials and compositions, such as, for example, adhesives, concrete and building materials, precast concrete parts and concrete ware which can be produced therefrom, such as, for example, pipes, wall segments or paving slabs, are frequently used in walls, in floors, in roofs and the like, or alternatively they are used for the production thereof. The cement-like materials are frequently exposed to water which can penetrate into the cement-like materials since such materials are generally porous. By using suitable aggregates or additives and formulations which can be prepared therewith, this inherent porosity can be reduced to a relatively great extent. However, complete avoidance of porosity cannot usually be achieved. An entire industry is therefore searching for methods which permit the materials mentioned above to be made water-repellent and hence to be protected from water.
Two methods have proved to be promising, an internal one and an external one. The internal method consists in adding a hydrophobing—water-repellent—substance or a reactive substance which produces a certain water-repellent effect after reaction or hardening is complete to a liquid mixture based on cement as a binder prior to hardening. Commercial substances which have been successfully used to date for this purpose are fatty acid-based materials, in particular stearates and oleates. For achieving good hydrophobing (water-repellent) effects, however, the addition of relatively large amounts of hydrophobing or reactive substances is necessary, and it is for this reason that a marked influence of these substances on the other material properties of the hardened cement-based materials cannot be ruled out.
Such a change in the other material properties can be substantially ruled out if external methods are used for hydrophobing. In these methods, the hydrophobing or reactive substances are applied to the hardened cement-based materials. Usually, low-viscosity substances or pastes are used, the active substances of which can penetrate into the pores, such as, for example, organosilicon compounds. The low-viscosity substances or pastes can be used, for example, in the form of aqueous emulsions. However, the low-viscosity substances or pastes can also be used as a mixture with other solvents or even directly if the organosilicon materials are sufficiently fluid per se. In order to achieve a sufficient water-repellent effect, multiple treatments of the cement-based materials are frequently necessary. This and the subsequent treatment of the hardened materials make the external method relatively complicated.
It has been proposed to add organosilicon materials as admixtures to cement-based mixtures in order to combine the good hydrophobing properties of these substances on the surfaces on subsequent external impregnation with the advantage of the easy use of stearates and oleates. The organosilicon materials have been used in the form of aqueous emulsions of hydrolysable silicon-hydrogen compounds.
In WO 02/090287, this method was further developed in that an aqueous emulsion of an organosilicon material, which emulsion has 0.25 to 4.5% by weight of alkoxysilanes and 0.1 to 2.0% by weight of alkoxysiloxanes, is added to a liquid cement-based mixture. The proportion of emulsion, based on the cement-containing composition, is 0.1 to 2%. The maximum proportion of organosilicon compounds in the cement-containing mixture is thus 6.5%×2%=0.13% by weight. The maximum proportion of organosilicon compounds in the cement-containing mixture is thus 0.35%×0.1%=0.00035% by weight. According to Example C of the aforementioned publication, an emulsion which has a solids content of 30% is diluted by addition of 9 parts of water. This dilute emulsion is used with a proportion of 1.1% by weight, based on the proportion of cement, in Example C. Thus, the proportion of organosilicon compounds, based on the cement-containing composition, is 0.033% by weight.
In addition to the damage to structures and building materials or products thereof by penetrating water, such as, for example, damage by frost, and leaching, salt displacement and spalling due to the formation of salt with water of hydration, which as a rule are suppressed by the use of in particular external water repellents, so-called efflorescence will also occur on various materials of the construction, e.g., exposed concrete, cast stones or bricks.
In addition to the purely aesthetic impairment of the overall visual appearance, for example in the case of concrete paving slabs or building facades, efflorescence phenomena on the material surfaces can also lead to limitations in the material properties, such as, for example, to a deterioration of the heat insulation properties or a decrease in the mechanical strength owing to leaching of the binder.
Secondary efflorescence is understood as meaning the effect that salts are dissolved by penetrating water and, by capillary transport, reach the surface where they remain as salt residue after evaporation of the water. This effect can be suppressed by subsequent hydrophobing.
However, efflorescence occurs even during the preparation of cement-bound systems, which cannot be suppressed by hydrophobing which is carried out subsequently. Efflorescence which occurs during the preparation is usually referred to as primary efflorescence. Primary efflorescence is presumably due to the fact that calcium hydroxide present is converted on the material surface with carbon dioxide from air into insoluble calcium carbonate.